Various packaging techniques have been used to build a load of unit products and subsequently wrap them for transportation, storage, containment and stabilization, protection and waterproofing. Products are often stacked as a load on a pallet to simplify handling of the products. The pallet load is commonly wrapped with stretch wrap packaging material. One system uses stretch wrapping machines to stretch, dispense and wrap stretch packaging material around a load. Stretch wrapping can be performed as an inline, automated packaging technique that dispenses and wraps packaging material in a stretch condition around a load on a pallet to cover and contain the load. Pallet stretch wrapping, whether accomplished by a turntable, rotating arm, or vertical rotating ring, typically covers the four vertical sides of the load with a stretchable film such as polyethylene film. In each of these arrangements, relative rotation is provided between the load and the packaging material dispenser to wrap packaging material about the sides of the load.
Stretch wrapping machines provide relative rotation between a stretch wrap packaging dispenser and a load either by driving the stretch wrap packaging dispenser around a stationary load or rotating the load on a turntable. Upon relative rotation, packaging material is wrapped on the load. Ring style stretch wrappers generally include a roll of packaging material mounted in a dispenser that rotates about the load on a ring. Vertical rings move substantially vertically between an upper and lower position to wrap film around a load. In a vertical ring, as in turntable and rotating wrap arm apparatuses, the four vertical sides of the load are wrapped, along the height of the load.
When pallet loads are wrapped, it is beneficial to wrap the film around the base of the load and at least a top portion of the pallet supporting the load in order to secure the load to the pallet. If the film is not wrapped around enough of the pallet, shifting of the load may occur during transportation of the load. In addition, it is also desirable to form a conventional rope of film at the base of the film web before applying it to the base of the load and the top portion of the pallet to provide additional resistance to load shifting. In order to form the conventional rope of film at the base of the load and wrap the base of the load and the pallet, the packaging material must be dispensed at a level below the base of the load.
In general, a packaging material dispenser supports a roll of packaging material a couple of inches above its base. In addition, the packaging material typically necks down one to two inches on both its top and bottom edges. Furthermore, one to two inches of clearance are required between the base of the packaging material dispenser and a load support surface (e.g., pedestal, conveyor, or floor) supporting the pallet and the load. Thus, in conventional stretch wrapping apparatuses, the lower edge of the packaging material is typically six to seven inches above the base of the pallet. Since most pallets are five to eight inches tall, there may be very little packaging material securing the load to the pallet.
To dispense the packaging material and create a rope at a level below the base of the load, the packaging material dispenser must be lowered sufficiently below the load such that the base of the roll of packaging material to be dispensed is below the base of the load. Certain types of stretch wrapping apparatuses, such as conventional turntable style machines, support palletized loads well above floor level, thereby providing sufficient clearance to lower the packaging material dispenser, and the base of the roll of packaging material, below the base of the load so that the packaging material can be applied to the pallet and the base of the load.
Other types of machines, such as overhead machines and low profile turntable machines, do not provide the clearance necessary to lower the packaging material dispenser below the base of the load. In overhead machines, a rotating arm that supports the packaging material dispenser must be able to clear the load support surface (e.g., pedestal, conveyor, or floor). In low profile machines, the top of a rotatable turntable is only a couple of inches above the floor, and there is not enough clearance for the packaging material dispenser, and thus the base of the roll of packaging material, to be lowered below the level of the base of the load. In machines such as these, it is necessary to drive the packaging material and the rope of packaging material to a level below the top of the pallet supporting the load.
Various techniques have been used in overhead machines in attempts to overcome this problem. Some prior art devices have tilted the packaging material dispenser, while others have tilted one or more idle rollers. See, for example, U.S. Pat. No. 5,875,617. Tilting the packaging material dispenser and/or idle rollers has had limited success in working the packaging material downward onto the pallet. Tilted roller concepts have had marginal success only, due to the sensitive nature of the tracking technique. For example, if the roller is tilted too far, the packaging material collapses into a total rope, and if the roller is not tilted far enough, the packaging material does not move downward enough to sufficiently cover the pallet. In addition, variation in packaging material surface, temperature, and wrap force make it difficult to maintain an angle that will lower the packaging sufficiently without narrowing it so much that many additional layers of wrap are required, decreasing wrap efficiency and increasing wrap cycle cost. Additionally If the film is successfully driven down below the last roller, the film will snag on the roller supporting mechanism and cause a film break.
Angled bars have also been used in an attempt to guide packaging material to a level below the base of the load. See, for example, U.S. Pat. No. 5,077,956. This technique has had little success due to the high forces incurred during stretch wrapping. The resultant friction is problematic in maintaining a constant wrap force and consistent packaging material guiding. Without complex and costly film feed force controls, friction build-up due to the tilted bars would break the packaging material when added to the friction normally experienced during stretch wrapping.
Other prior art techniques include “dropping down” a conveyor around a palletized load to leave the palletized load on a pedestal, providing sufficient clearance to lower the packaging material dispenser, including the bottom of the roll or packaging material, below the level of the base of the load. Alternatively, some conveyor designs “pop up” the palletized load, raising it sufficiently above the conveyor to provide clearance for lowering the packaging material dispenser, including the base of the roll of packaging material, below the level of the base of the load. These are complex mechanical systems that are costly to maintain.
A conventional rope of packaging material is created when the base or bottom portion of the packaging material is moved over a conventional roping mechanism, such as a wheel or fixed horizontal bar. The conventional roping mechanism pushes the base or bottom portion of the packaging material upward into itself, gathering the base or bottom portion of the packaging material into a structure commonly referred to as a conventional rope of packaging material. As discussed above, the conventional rope may be wrapped around the base of the load to secure the packaging material layers to the load, thereby improving load containment. In conventional ropes, the bottom portion of the packaging material is gathered, i.e., pushed together in accordion-like fashion. Only the packaging material's tackiness holds the gathered packaging material together, and thus, a conventional rope does not have any structural integrity. Thus, it is common for portions of a conventional rope of film to come undone or loosen during or after the wrapping process. For this reason, there is a need for a rope structure that is capable of retaining its structural integrity during the wrapping process and after the wrapping process, when the load is subject to various forces during shipping.
It is accordingly a primary object of the invention to provide a method and apparatus for rolling packaging material into a rolled cable before applying it to the base of a load and the top portion of a pallet to further secure the load to the pallet.
It is an additional object of the present invention to provide a method and apparatus to reduce the complexity and cost associated with rolling a portion of a web of film into a rolled cable.